feat(notifications): add sub-agent system notification toggle #1304

Job	Run time
typecheck	25s
lint	26s
test-js	1m 0s
Rust tests (macOS)	1m 43s
Rust tests (Linux)	5m 36s
Rust tests (Windows)	6m 21s
Tauri build (${{ matrix.platform.name }})	-1s
	15m 30s

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